1. Field of the Invention
The present invention relates generally to semiconductor devices, and more particularly relates to lateral diffused metal-oxide-semiconductor (LDMOS) devices.
2. Description of the Prior Art
Processing technologies and device structures for forming integrated circuits (ICs) are often implemented using a plurality of interconnected field effect transistors (FETs), also called metal-oxide-semiconductor (MOS) field effect transistors (MOSFETs), or simply MOS transistors or devices. A well-known subset of MOS transistors is referred to as lateral diffused metal-oxide-semiconductor (LDMOS) transistors or devices. Although the abbreviation “MOS” and the term “MOS device” literally refer to a device having a metal gate electrode and an oxide gate insulator, that term will be used throughout to refer to any semiconductor device that includes a conductive gate (whether metal or not) that is positioned over a gate insulator (whether oxide or other dielectric) which, in turn, is positioned over a semiconductor substrate. Accordingly, the term metal-oxide-semiconductor and the abbreviations “MOS” and “LDMOS” are used herein even though such devices may not employ just metals or oxides but conductive materials other than metals, and insulating materials other than oxides. Accordingly, as used herein, the terms MOS and LDMOS are intended to include such variations. Non-limiting examples of conductive materials suitable for use in MOS and LDMOS devices are metals, metal alloys, semi-metals, metal-semiconductor alloys or compounds, doped semiconductors, and combinations thereof. Non-limiting examples of insulating materials suitable for use in MOS and LDMOS devices are oxides, nitrides, oxy-nitrides mixtures, organic insulating materials and other dielectrics.
A typical MOS transistor includes a gate “control” electrode and spaced-apart source and drain electrodes between which a current can flow. A voltage applied to the gate controls the flow of current through a conductive channel region induced in the underlying semiconductor between the source and drain. In an LDMOS device, a drift space is provided between the channel region and the drain. In some cases a shallow trench isolation (STI) region or field oxide (e.g. made from an insulator such as an oxide or other dielectric material) is provided in the drift space between the channel region and the drain, in which case the channel current passes underneath the STI region. This type of LDMOS is called “field LDMOS”.
However, there are still some problems in a conventional LDMOS device such as relatively high on-resistance of the device and inevitable parasitic loss due to parasitic capacitance. Therefore, there is a need to provide an improved LDMOS device so as to overcome aforementioned problems.